The invention relates to a screw with a screw body having a thread.
A self-locking and/or vibration-proof connecting member in the form of a locking screw is known, which has a three-lobed geometry of the thread body with a special thread flank angle of 60.degree./30.degree.. A threaded locking screw constructed in this way is automatically locked in a nut or taphole made from steel, sheet metal or other suitable materials. This is due to the clamping force of the three-lobed thread crests on the metal of the counter-thread and through the intimate contact of the 30.degree. crests on the three-lobed screw periphery with the counter-thread, which prevents longitudinal or transverse movements between the screw and e.g. the nut. Such threaded locking screws are not loosened by oscillations and vibrations. However, it has been found that although such threaded locking screws ensure a high vibration resistance and secure the screw in a completely adequate manner, no seal against the penetration of liquids such as water, hydraulic oil, etc. is ensured. Liquid penetrates between the thread of the locking screw and the counter-thread.
In addition, a screw is known, which forms its own counter-thread without cutting by plastic or ductile working and is constructed in such a way that the screw has a three-lobed geometry of the thread body with a flank angle of 60.degree.. The counter-threads extend over a length of approximately 3 pitches towards the screw end, whilst retaining their marked geometry and the tip of the flank angle of 60.degree.. In order to improve the positioning in the hole and of the screw shoulder, the tip was further developed in such a way that for the first three to four threads of the screw tip the screw is constructed with a smaller diameter, whilst retaining the three-lobed thread shape. In the thread constructions the dimensions of the envelope circle of the three-lobed shape and the 60.degree. flank angle of the thread body are selected in such a way that interchangeability of the shaped nut thread with a screw standard is ensured after screwing up and unscrewing. A screw constructed in this way shapes its own counterthread without cutting, so that there is no need to cut the nut thread. On tapping this screw, the fibre flow in the counter-thread is sealed and workhardened by cold working, the material flowing in clearance-free manner round the thread flanks of this screw without any pitch errors.